M.~Heuer, G.~Lichtenberg, S.~Pfeiffer, and H.~Schlarb, "Comparison of Feedback Controller for Link Stabilizing Units of the Laser Based Synchronisation System used at the European XFEL", in Proc. 3rd International Beam Instrumentation Conference, Monterey, CA, USA, paper MOCZB3, pp. 34–38, ISBN: 978-3-95450-141-0, \url{http://jacow.org/IBIC2014/papers/moczb3.pdf}, 2014.